This disclosure relates to count loss correction in nuclear imaging. For example, quantization in single photon emission computed tomography (SPECT) imaging uses count loss correction to provide more accurate estimates of activity in the patient. The detector front-end signal processing and discriminator may cause undercounting of events due to dead time. The dead time (also called a count loss) of a nuclear imaging system or gamma camera is the time during which the system processes one or more events and is not available to process succeeding or concurrent events. The electronic circuits in a nuclear imaging system and the complex interaction between such circuits result in dead time.
Because of the dead time phenomenon, the rate at which events are processed by the system is a non-linear function of the rate of incoming events. Furthermore, the count rate losses also depend on the total number of emissions produced, including those emissions that lie outside the energy window of the channel analyzers of the system. Thus, the dead time of a nuclear imaging system depends on the nature of the system and the type of field interacting therewith.
In one approach to compensate for the dead time, the true rate as a function of apparent rate is empirically measured for a system that approximates a clinical system. This relationship of actual to apparent is stored in a look-up table (LUT). The front-end count rate for future patients is then estimated by using the look-up table (LUT). For example, a count rate achieved by the SPECT system is correlated to loss using the lookup table (LUT).
Since this approach is time-invariant or case-in variant, it reduces the accuracy of the count loss correction. Dead time is extremely complicated and is dependent not only on the inherent limitations of the nuclear imaging system itself but also on the nuclear spectra with which the system is interacting. Consequently, the use of an empirical function to compensate for dead time introduces error or fails to account for variation. Any nuclear imaging system aspects that are time varient or use-case varient may reduce the accuracy of the count loss correction.